An investigation's underway into the cause of the fatal weekend plane crash in Otago

One person was killed and another critically injured, when their aircraft encountered trouble on Saturday afternoon near Lake Hawea - north of Wanaka.

The pair were taking part in the annual Autumn Fly-In for the Aircraft Owners and Pilots Association, alongside dozens of other aviators.

President Sue Kronfeld says they can't speculate themselves on what went wrong, as that's for Police and aviation authorities to investigate.